Tonight, Channel 4 reveals a startling aspect of teenagers' sex lives: pornography. Schoolchildren, it appears, are big consumers of porn. A new series, The Sex Education Show v Pornography, shows how teenagers' sexual attitudes, behaviour and hang-ups are influenced by so-called adult entertainment. One doesn't have to be a prude to find this all very unsettling.

Consider some findings from tonight's episode, based on a survey of over 400 pupils, aged 14 to 17, in four schools in the south and west of England. The average teenager, the survey suggests, claims to watch 90 minutes of porn a week. Mobile phones and the internet, despite supposed controls and content filters, make porn-sharing all too easy. Their viewing includes bestiality, group sex and lesbian intercourse. "Porn," says one boy, "is everywhere."

Three in 10 pupils say they learn about sex from porn. Yet porn actors never use contraception on camera. For all the bravado, there's an undercurrent of ambivalence. Asked whether "pornography might give boys or girls false ideas about sex", 60% said yes. A 14-year-old girl reflects: "Pornography puts a lot of pressure on girls. A boy will see it and think this woman is gonna do this."

A group of boys from Sheringham high school in Norfolk is shown photographs of 10 pairs of breasts. All say the most attractive are the ones that have been surgically enhanced. Alarmingly, a posse of their female classmates says the same thing. Both sexes are unimpressed with normal breasts, which – unlike porn stars' silicone-boosted chests – are often not symmetrical and sit down, not up.

Similarly, when the programme makers show boys and girls a woman opening her legs to reveal hair, there are gasps, some born of disgust. In porn, females are always shaved down below. Girls admit that they are starting to shave their lower regions and that boys expect them to do so. The pupils' reaction shows how their expectations of what bodies should look like are framed by watching porn. Freakish ideas of physicality are now mainstream.

Unsurprisingly, 45% of girls at Sheringham are unhappy with their breasts and almost a third would consider surgery. Boys are victims in their own way too, though. As the presenter, Anna Richardson, says: "Teenage boys told us that they feel very anxious about the size of their penises, because they're being influenced by porn. They're very anxious about their performance as and when they do come to have sex because they see what happens in porn and think, 'Well, that's how it's meant to be'." Richardson says she found making the series "distressing and disturbing".

If you are concerned about the sexualisation of children and the environment, this series should be required viewing.